The field coil wires in the present type of electric motor are wound on the pole pieces and the ends are connected to terminals supported by the terminal block. The coil is wound and the connection of the wire to the terminals is handled by robotic machines. The final connection of the wire to the terminal is secured by crimping the terminal tang into the wire, and the connection is then fused by known technology to securely fix the wire to the terminal.
Most motors are not subjected to significant vibration but when the motor is used in certain kinds of hand tools the motor is subjected to substantial vibration or shock caused by the nature of the tool, such as hammer-drills, impact wrenches and rotary hammers. This impact or vibration causes relative movement between the terminal and the coil and this results in small but damaging flexure of the wire, leading to breakage of the wire which, of course, shuts down the motor and the tool. The breakage occurs approximately where the wire enters the tang. The wire enters the space between the tang and the terminal at essentially 90.degree.. The fusing process heats the copper wire enough so that it hardens and the pressure of the fusing tool against the tang coupled with the heat causes the wire to melt down a little bit at the point where the wire enters the space between the tang and the terminal. The combination of necking down and heating and hardening the wire, coupled with the vibration, sets up a combination of factors leading to breakage of the wire.